@@ -20,30 +20,51 @@ %% WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING %% FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR %% OTHER DEALINGS IN THE SOFTWARE. - +%% +%% Change Log +%% * 2008-10-15 ngerakines, v0.2 +%% - Added edoc friendly documentation. +%% - Added a patch submitted by Sergei Matusevich. +%% - Misc module organization and layout changes. +%% +%% @author Nick Gerakines <nick@gerakines.net> [http://blog.socklabs.com/] +%% @copyright 2008 Nick Gerakines +%% @doc A module that provides basic geohash encoding and decoding. -module(geohash). --compile(export_all). + +-export([encode/2, encode/3, decode/1]). -author("Nick Gerakines <nick@gerakines.net>"). --version("0.1"). +-version("0.2"). --include_lib("eunit/include/eunit.hrl"). +-ifdef(TEST). -%% - -%% Unit tests +-include_lib("eunit/include/eunit.hrl"). geohash_test_() -> Tests = [ {42.6, -5.6, "ezs42"}, {-20, 50, "mh7w"}, {10.1, 57.2, "t3b9m"}, {49.26, -123.26, "c2b25p"}, {0.005, -179.567, "80021bgm"}, {-30.55555, 0.2, "k484ht99h2"}, {5.00001, -140.6, "8buh2w4pnt"}], - [?_assert(geohash:encode(A, B) == C) || {A, B, C} <- Tests], - % [?_assert(geohash:decode(C) == [A, B]) || {A, B, C} <- Tests], - ok. + [?_assert(encode(A, B) == C) || {A, B, C} <- Tests]. + +-endif. + +%% @doc Create a hash for a given latitude and longitude. +encode(Lat, Lon) when is_number(Lat), is_number(Lon) -> + Pres = precision(Lat, Lon), + encode(Lat, Lon, Pres). -%% - -%% Base32 encoding +%% @doc Create a hash for a given latitude and longitude with a specific precision. +encode(Lat, Lon, Pres) when is_number(Lat), is_number(Lon), is_number(Pres) -> + encode_major(Pres, {Lat, Lon}, {{90, -90}, {180, -180}}, 1, []). +%% @doc Decode a geohash into a latitude and longitude. +decode(Hash) when is_list(Hash) -> + Set = decode_interval(Hash), + [mid(X, Set) || X <- [0, 1]]. + +%% @private base_32() -> [ {0, $0}, {1, $1}, {2, $2}, {3, $3}, {4, $4}, {5, $5}, {6, $6}, {7, $7}, {8, $8}, {9, $9}, {10, $b}, {11, $c}, {12, $d}, {13, $e}, {14, $f}, @@ -52,86 +73,82 @@ base_32() -> [ {29, $x}, {30, $y}, {31, $z} ]. -encode_base32(X) -> {value, {_, Y}} = lists:keysearch(X, 1, base_32()), Y. - -decode_base32(X) -> {value, {Y, _}} = lists:keysearch(X, 2, base_32()), Y. - -%% - -%% encode functionality +%% @private +encode_base32(X) when is_integer(X), X > -1, X < 32 -> + {value, {_, Y}} = lists:keysearch(X, 1, base_32()), + Y. -encode(Lat, Lon) -> - Pres = geohash:precision(Lat, Lon), - geohash:encode(Lat, Lon, Pres). - -encode(Lat, Lon, Pres) -> - geohash:encode_major(Pres, {Lat, Lon}, {{90, -90}, {180, -180}}, 1, []). +%% @private +decode_base32(X) when is_integer(X) -> + {value, {Y, _}} = lists:keysearch(X, 2, base_32()), + Y. +%% @private encode_major(0, {_Lat, _Lon}, _Set, _Flip, Acc) -> lists:reverse(Acc); encode_major(X, {Lat, Lon}, Set, Flip, Acc) -> - {Code, NewSet, NewFlip} = geohash:encode_minor(0, {Lat, Lon}, Set, 0, Flip), + {Code, NewSet, NewFlip} = encode_minor(0, {Lat, Lon}, Set, 0, Flip), encode_major(X - 1, {Lat, Lon}, NewSet, NewFlip, [Code | Acc]). +%% @private encode_minor(5, _, Set, Bits, Flip) -> {encode_base32(Bits), Set, Flip}; encode_minor(X, {Lat, Lon}, Set, Bits, Flip) -> - Mid = geohash:mid(Flip, Set), - Bit = case geohash:latlon(Flip, {Lat, Lon}) >= Mid of true -> 1; _ -> 0 end, + Mid = mid(Flip, Set), + Bit = case latlon(Flip, {Lat, Lon}) >= Mid of true -> 1; _ -> 0 end, NewBits = (Bits bsl 1) bor Bit, - NewSet = geohash:shiftset(Set, Flip, Bit, Mid), - encode_minor(X + 1, {Lat, Lon}, NewSet, NewBits, geohash:flip(Flip)). - -%% - -%% decode functionality - -%% [ X / 10000000 || X<-geohash:decode("ezs42")] -%% [ X / 10000000 || X<-geohash:decode("8buh2w4pnt")] -decode(Hash) -> - Set = decode_interval(Hash), - [mid(X, Set) || X <- [0, 1]]. + NewSet = shiftset(Set, Flip, Bit, Mid), + encode_minor(X + 1, {Lat, Lon}, NewSet, NewBits, flip(Flip)). +%% @private decode_interval(Hash) -> M = 1, decode_major(Hash, 1, {{90 * M, -90 * M}, {180 * M, -180 * M}}). +%% @private decode_major([], _Flip, Set) -> Set; decode_major([Char | Chars], Flip, Set) -> Bits = decode_base32(Char), - {NewSet, NewFlip} = geohash:decode_minor(0, Set, Bits, Flip), + {NewSet, NewFlip} = decode_minor(0, Set, Bits, Flip), decode_major(Chars, NewFlip, NewSet). +%% @private decode_minor(5, Set, _Bits, Flip) -> {Set, Flip}; decode_minor(X, Set, Bits, Flip) -> - Mid = geohash:mid(Flip, Set), + Mid = mid(Flip, Set), BitPos = (Bits band 16 ) bsr 4, - NewSet = geohash:shiftset(Set, Flip, BitPos, Mid), - decode_minor(X + 1, NewSet, Bits bsl 1, geohash:flip(Flip)). - -%% - -%% private methods + NewSet = shiftset(Set, Flip, BitPos, Mid), + decode_minor(X + 1, NewSet, Bits bsl 1, flip(Flip)). +%% @private flip(0) -> 1; flip(_) -> 0. +%% @private shiftset({{A, B}, {_, D}}, 1, BitPos, New) when BitPos == 0 -> {{A, B}, {New, D}}; shiftset({{A, B}, {C, _}}, 1, 1, New) -> {{A, B}, {C, New}}; shiftset({{_, B}, {C, D}}, 0, BitPos, New) when BitPos == 0 -> {{New, B}, {C, D}}; shiftset({{A, _}, {C, D}}, 0, 1, New) -> {{A, New}, {C, D}}. +%% @private latlon(0, {X, _}) -> X; latlon(1, {_, X}) -> X. +%% @private mid(0, {{A, B}, _}) -> (A + B) / 2; mid(1, {_, {A, B}}) -> (A + B) / 2. +%% @private d2b(X) -> round((X * 3.32192809488736)). +%% @private bit_for_number(N) when is_float(N) -> [RawChars] = io_lib:fwrite("~f", [N]), [_ | [FChars]] = string:tokens(string:strip(RawChars, right, $0), "."), - geohash:d2b(length(FChars)); + d2b(length(FChars)); bit_for_number(_) -> 0. +%% @private precision(Lat, Lon) -> - Lab = geohash:bit_for_number(Lat) + 8, - Lob = geohash:bit_for_number(Lon) + 9, + Lab = bit_for_number(Lat) + 8, + Lob = bit_for_number(Lon) + 9, Lux = case Lab > Lob of true -> Lab; _ -> Lob end, round(Lux / 2.5). geohash.erl 0a7acb68978235a15f704fd8dbec730ddac0e9bf Nick Gerakines nick@gerakines.net http://github.com/ngerakines/erlang_geohash/commit/bb035e03d6120660ccf17b41f3cd7e4fe53a3c35 bb035e03d6120660ccf17b41f3cd7e4fe53a3c35 2008-10-15T16:55:25-07:00 2008-10-15T16:55:25-07:00 Bumping to 0.2. Added patch by Sergei Matusevich for cleaner base32 encoding and decoding. 1d99202fd093b5589213d818902191a250a23455 Nick Gerakines nick@gerakines.net